November 2002 Cainozoic Research, 1(1-2X2001), pp. 3-12,

The mesogastropod Littorina littorea (Linné, 1758) in : palaeobiogeography and migration

Ólöf+E. Leifsdóttir & Leifur+A. Símonarson

University ofIceland, Science Institute, Dunhaga 3, 107 Reykjavik, Iceland; e-mail: [email protected], and [email protected]

Received 5 April 2001; revised version accepted 29 September 2001

in Atpresent, the periwinkle, Littorina littorea (Linné, 1758), is not found living Iceland. The only confirmedoccurrence of the

in Icelandic sediments is in the Middle upper littoral conglomerate at Búlandshöfdi, Snaefellsnes, West Iceland. These layers

were deposited during an interglacial stage, slightly older than 1.1 Ma. The species apparently evolved from the Pacific L. squalida Bro-

& derip Sowerby, 1829, after the trans-Arctic/North Atlantic migration from the Pacific, possibly in response to cooling and increasing

2.55 environmental energy. The oldest occurrence of L. littorea is in the British , between and 2.4 Ma; it is unknown from the Tjörnes deposits in N Iceland, older than 2.6 Ma. This indicates that the species separation postdates the

deposition of the uppermost Serripes Zone of Tjörnes, after the tide of the migration wave passed Iceland, but before it reached the The taxonomic and of North Atlantic molluscs area and Britain, between 2.6 and 2.4 Ma. diversity palaeobiogeography were about greatly affected by the major climatic changes that resulted in an extensive glaciation at 2.5 Ma.

Key words: Mesogastropoda,Littorina, Iceland, MiddlePleistocene, speciation, palaeobiogeography, migration.

Introduction Growth lines are distinctly prosocline and form an angle of

about 120° with the axis of the spire. Spiral ridges and

The prosobranch mesogastropod Littorina littorea was grooves are slight and numerous, and especially marked in

described Linne who named it Turbo but tend to become obscure in older originally by (1758), young individuals, established the The ribs low and The littoreus. In 1822, Ferussac genusLittorina, ones. numerous are very narrow.

T. littoreus being its type species now. Since the times of aperture is oval and angulate in the uppermost part and lies

these workers, there have been a number of incorrect in a prosocline plane with the peristome. The outer lip

spelling and minor nomenclatorialcomplications, but these meets the periphery of the body at an angle of 125-130° to

will not be enumerated here. Several doubtful records of the axis. The inner lip is thick and lacks an umbilical

fossil exist in Iceland. The aim of the The white columella is short and inclined towards living and Littorina groove. of shell’s axis. Colours of the shell from present study is to attempt to clear up the occurrence L. the vary cream to

littorea in Iceland and to provide a more precise picture of brown, black, brownish black, grey, orange or red, but

the palaeobiogeography of the species. usually the shell is pale brown with 8-25 narrow black to

The material studied comprises specimens collected by dark brown lines. The body whorl is around80-85% ofthe

in and total ofthe shelland the ofthe is 60- the authors, as well as specimens kept geological height height aperture littorea zoological museums in Iceland and Denmark. 70%. The adult shell of L. is the largest of the ge-

nus with a mature shell height between 10.6 and 52.8 mm

Abbreviationsused in the text are as follows: (Reid, 1996). The protoconch consists of two or more

unsculpted whorls (Fretter & Graham, 1980). The snout is

IMNH Icelandic Museum of Natural History, Reyk- broad, slightly tapered and distally truncated. The terminal

mouth is ventral the head and has radula with javik. slightly on a

NHM The Natural History Museum, London. a relative length from 1.49 to 2.15 mm (Reid, 1996). The

cephalic tentacles each have an eye on a lateral bulge at the

base. The foot is elongated and shield-shaped. The oper-

culum has 2-3 and nucleus the colu- Diagnosis turns a displaced to

mellar side. There is a linear osphradium and a long gill in

the mantle to the left. The with 10-42 mamil- The typical adult shellof L. littorea is solid with a pointed, cavity penis, liform is and cyrtoconoid spire and 5-6 whorls, which are slightly tumid glands, sickle-shaped tapers abruptly distally. Vermeij (1982) found some patterns in shell thickness to nearly flat in profile (Figure la, b). The upper part ofthe scale. the on a geographical body whorl is straight to concave, especially near ap-

erture. The suture is shallow, resulting in a flat perimeter. -4-

Figure 1. Species ofLittorina.

a L. littorea(IMNH 754), Recent specimenfrom Rorvig, Denmark; b L. littorea (IMNH 755), from Middle Holocene Stone Age sea deposits in Denmark; c,d L. littorea (IMNH 756), from MiddlePleistocene interglacial deposits at Bulandshofdi (W Iceland); e,f L squalida (IMNH 3976), from horizon 11 ofthe Pliocene Mactra Zone ofthe Tjomes beds, N Iceland (afterReid, 1996); g,h L. islandica (IMNH 3977, paratype), from horizon 25 of the Pliocene Serripes Zone of the Tjomes beds, N Iceland (after Reid,

1966).

In North America, the shells become thinner to the south of population has recently been discovered at Castiglioncello,

Cape Cod, which indicates a relationship between tem- NW Italy (Barsotti & Campani, 1982). perature, growth rate and shell form. In brackish habitats, In the western Atlantic, L. littorea is distributed from

shells are both smaller and thinner with a fainter texture, the Strait of Belle Isle (Newfoundland) in the north to Vir- and the spire height seems to increase with decreasing ginia in the south. The coast of Connecticut is the most

salinity (Reid, 1996). southerly suitable habitat, but occasionally currents trans- south far mid-New and the port larvae as as Jersey Del-

Recent distribution marva Peninsula where settlement sometimes occurs (Reid,

1996). According to Vermeij (1982), the southernmost

Littorina littorea is widely distributed on European shores occurrence seems to have been at Wachapreague in Vir-

(Figure 2) from the White Sea in the north to southern ginia.

Portugal in the south (Fretter & Graham, 1980; Reid, In the East Pacific, the species has been recorded from

1996). The most northerly record from southern Svalbard the Puget Sound (Washington), San Francisco Bay and confirmed. The Trinidad these the has (Rozycki, 1991) has not yet been species Bay (California). In places, species Bornholm. Further south it able The extends into the Baltic as far as not been to establish populations (Reid, 1996).

is common along the French Atlantic coast as far as lie vertical range is from 0 m at several localities, to a depth of

d’Oloron. The southern limit in the eastern Atlantic is about 60 m in northern Britain and Skagerrak (Fretter &

close to Algarve in southern Portugal. There are some Graham, 1962, 1980; Reid, 1996). The species prefers the

doubtful records from the Mediterranean, but a breeding intertidalzone. -5 -

of been Figure 2. Recent distribution Littorina littorea. Triangles mark either unverified finds or occurrences where the species has not

able to produce established populations. The regional division of northern European seas is based on Feyling-Hanssen (1955), as

modifiedby Simonarson et al. (1998).

littorea recorded from found Littorina was Greenland by ‘Some few specimens not more than 15 mm long are

Fabricius (1780), but that was a misidentification of L. in the Museum of Christian VIII labelled "ex Islandia, saxatilis (Olivi, 1792). Another Greenland record was Johnsen", but it seems probable to me that a confusion has based on incorrectly localised material (Reid, 1996). The taken place’. These four specimens are still in the Zoologi-

species was recorded three times from the Faroe Islands in cal Museum (Copenhagen). They are all without the 19th century, but it has not been found again despite and so fresh looking that they are probably not of subfossil

further collectionefforts (Morch, 1868; Sparck & Thorson, origin (Thorson, 1941). Furthermore, one shell is labelled

1933). Tsld Steenstrup’ and Thorson (1941, p. 34) came to the Turbo first mentioned ‘ subfossiT. The collection From Iceland, littoreus was by conclusion, that it could be

Mohr (1786). However, it is quite clear from his descrip- also contains two more shells from Iceland labelledLitto- tion that he was actually dealing with L. obtusata (Linne, rina littorea. One was found in the tidal zone of Isafjordur

1758) and L. saxatilis, without separating them. Then (NW Iceland) and the other among stones on the shore in

Morch (1868, p. 207) stated (in Danish, here translated), Amarfjordur (also NW Iceland). These shells are in the -6-

and 6-7 weeks & The Zoological Museum (Copenhagen), our re- even (Fretter Graham, 1980).

to saxatilis. reach of 20 examinationhas revealedthey all belong L. may an age nearly years (Woodward, 1913).

Furthermore, it looks like some mixup took place when the shells from Isafjordur and Amarfjordur were labelled at the museum, as Johansen (1901), who found them, re- Fossil occurrence ferred to them as L. groenlandica Menke, 1830 and L. rudis (Maton, 1797). Finally, it should be mentionedthat The stratigraphical range of L littorea is apparently from

found in old Danish that the Pliocene the For the Plio-Pleistocene shells of L. littorea were an ship to present day.

Iceland. The the between the Reuverian and stranded on Flatey in Breidafjordur, West boundary we use boundary the of The the shells probably came with ballast in the ship from Den- Praetiglian stages Netherlands, at beginning of the first in the Northern mark (Oskarsson, 1973). These are the only known records major glaciation Hemisphere, in and of L. littorea from Iceland, and since no living specimens since this is commonly used northern western have been collected from Icelandic waters it probably does Europe (Zagwijn, 1992; Morrison & Kukla, 1998;

Simonarson The of this is close not live there at present. et at., 1998). age boundary

to 2.5 Ma(Funnell, 1995, 1996).

The oldest occurrence of L. littorea was recorded from

the middle of the Red Crag Formation of Ecology and biology part (Wood, 1848), subsequently confirmed by Reid (1996),

where it is rare in the Newboumian and the Butleyan crags

Littorina littorea prefers a stable substrate within the inter- (Harmer, 1920). It is not known from the Waltonian Crag, where it is characteristic inhabitant tidal zone a epifaunal taken to be the oldest memberof the Red Crag Formation, shores. of all but the most exposed rocky It usually occurs dated at about 2.55 Ma (Funnell, 1996). The Ludham on rocks between the high-water mark of neap tides and Member, the youngest unit of the upper Red Crag Forma- the low-water mark of found in extreme spring tides, being tion, has been dated at c. 2.4 Ma, so it seems that the for- the of Fucus and Laminaria It algal zones (Reid, 1996). mation was deposited during Early Pleistocene time, with also the surface of mud less occurs on wet or, frequently, the exception of the Waltonian Crag, which is of latest solid allow firm attachment on where objects (Fretter Pliocene et 1991; Funnell, age (Gibbard al., 1996). extends & Graham, 1980; Reid, 1996). It sublittorally to In continental Europe, fragments of L. littorea have

depths of about 60 m, especially in the colder and more been collected from the Ouwerkerk borehole (Zeeland) in

ofits However, the maximum northerly parts range. depths sediments of an age corresponding to the Belgian Merk- are recorded from approximately the middle of its distri- semian Stage, although contamination from overlying de- bution in the eastern Atlantic & range (Fretter Graham, posits cannot be ruled out (Reid, 1996). The species is 1980). abundant in the Norwich Crag Formation, which overlies

The species tolerates rather high temperatures, more so the Red Crag in East Anglia and is dated at 2.0 to 1.6 Ma in air than in Sandison that the ani- also is water. (1967) reported (Gibbard & Zalasiewicz, 1988; Funnell, 1996). It a mal falls into 32°C in air and 31°C in a coma at water. common fossil in boreholes penetrating contemporaneous deathoccurred 42°C in air and 40°C in for Heat at at water deposits in the southern Netherlands, as well as in wells in specimens from the Firth ofForth, and Evans (1948) gave the middle Tiglian Maas-sluis Formation at Roosendaal for in When 39°C and 46°C those Cardigan Bay. tem- (Reid, 1996). Furthermore, it occurs in the Mya arenaria-

below 8°C, most become inac- ulvae of similar in the and perature drops specimens Hydrobia Zone age western tive. ofthe winter without of Netherlands Gibbard They spend part feeding (Fretter central parts the (Spaink, 1975; et

& Graham, 1980); many appear to migrate down to the al., 1991). A few specimens ofL. littoreahave been found shore to avoid cold (Gendron, 1977). in the Baventian marine clay bed at Covehithe (), river and Littorina littorea frequently occurs at mouths, probably representing the first cold stage of truly glacial

far into estuaries and may penetrate fjords, surviving at intensity in the English marine, Early Pleistocene succes- salinities down to 9-10%o (Fretter & Graham, 1980). sion (West et al., 1980). In Morocco, the species occurred Arnold that the active of (1972) reported movement living as far south as Cape Rhir during cold periods of the Mid- specimens apparently decreased markedly at salinities dle Pleistocene (Reid, 1996). below 20%o in SW Wales (Milford Have, the Daucleddau) Littorina littorea is common in several raised beach and eastern Canada. deposits from the Late Pleistocene in Britain and in conti- The is omnivorous species mainly an grazer, feeding nental Europe (Reid, 1996). It is of common occurrence in wide of and detritus, on a range algae, , vegetable the Eemian zones of Denmark and the Netherlands it takes animal detritus & Gra- but occasionally (Fretter (Harmer, 1923), as well as in Upper Pleistocene strata ham, 1980; Reid, 1996). around the White and Barents seas (Knipowitsch, 1900;

Littorina littorea is oviparous with planktotrophic de- Merklin et al, 1979). Furthermore, one specimen has been

Each female about 500 velopment (Reid, 1996). lays cap- found on Taymyr Peninsula (N Siberia, latitude 32°N), in a sules which burst after 5-6 and release veli- at a time, days deposit from the Kazan-sevskaga Transgression, of about weeks ger larvae, which swim in the plankton for 4-5 or 100,000 years old (Reid, 1996). -7-

Figure 3. Distribution offossil Littorina littorea.

The species is common in Upper Pleistocene (late gla- shell was collected from a deposit of Middle Wisconsian

and Holocene sediments southern cial) in Scandinavia, age, 33,000-44,000 years old (Wagner, 1977). Addition- such as the deposits from the Middle Holocene Littorina ally, specimens have been collected in Indian middens in Sea. This had elevated sea an sea temperature and higher the Canadian Maritimes, dated at 500-1,000 BP (Reid, than and this salinity prevailing at present, during time the 1996). In northern Newfoundland, two specimens have far into the where it species penetrated Baltic, was very been found at a site ofNorse settlement. A few shells have the common. In Svalbard, species is considered a good also been found in Nova Scotia and New Brunswick which index fossil for littoral deposits from the Middle Holocene have been radiocarbon-datedbetween 1,000 and 1,500 BP warm period (Feyling-Hanssen, 1955). (Clarke & Erskine, 1961). littorea has been found in North but Littorina America, Thus, L. littorea has been recorded as a fossil from the Pleistocene record is from SW Scotia. The only Nova several places outside the present area of distribution, -8-

which indicates shifts in geographical range, apparently specimens of L. littorea that Gladenkov et al. (1980) re-

linked to climatic oscillations (Figure 3). One of these corded from the Serripes Zone were ascribed by Reid

is but the Icelandic will be dealt places Iceland, occurrence (1996) to a new species, L. islandica, having more distinct

with below. ornament to sutures and an of rounded ribs, of which up

three may become more prominent and carinate than in L.

littorea (Figure Ig, h). Thus, Reid (1996, p. 247) con- Occurrence in Iceland cluded, when dealing with L. islandica, that, ‘The only

other Littorina species recorded as a Pliocene fossil from

Iceland is The authors have Morch (1871) recorded L. littorea from the Pliocene Ser- .... L. squalida.' present

reached the same conclusion regarding the identification of ripes Zone of the Tjomes beds in northern Iceland. Much Littorina from the beds, that L. littorea has later, Gladenkov et al. (1980) recorded it from horizons 10 Tjomes namely been foundthere. and 12 of the older Mactra Zone and horizons 18, 23 and not yet Thoroddsen (1892) recorded L. littorea from two 25 of the younger Serripes Zone, following the division of Lower Holocene littoral the Urridafoss Falls Bardarson(1925) (see also Figure 4). deposits near in the Thjorsa River (S Iceland), and by the Laxa River in

Hvammsfjordur (W Iceland). These sites are 31 m and 20-

26 m above sea level, respectively, and shell material from

the latter has been radiocarbon-dated as 9,755±90 BP and

9,765±90 BP (Norddahl & Asbjomsdottir, 1995). Despite

extensive studies at these localities no shells of L. littorea

have but been found, rather several specimens of L. saxa-

tilis. In a single sample from Mjohylur we found 39 speci-

mens of the species, or 35.4% of the sample (Jonsdottir &

Bjomsdottir, 1995). Therefore, our opinion is that

Thoroddsen’s records were based on misidentification of

L. saxatilis. Unfortunately, Thoroddsen’s material has not

been traced for a re-examination.

The records of Spjeldnaes & Henningsmoen (1963) and Reid from the Middle (1996) Holocene warm period Iceland in are obviously based on Thoroddsen’s above-

mentioned samples reported in 1892. Therefore, some

mixup in time has apparently taken place, as these samples

are from Lower Holocene deposits and not from the Mid-

dle Holocene warm period. We have identified several

shell samples from Icelandic sediments deposited during

the Middle Holocene climatic optimum and have never

found L. littorea in any of them. Some of these samples

consist of to 800 of up specimens Littorina (Leifsdottir &

Simonarson, 1999). Therefore, we assume that L. littorea

did not live in Iceland during the Holocene.

The last record of L. littorea from Iceland is that of

Leifsdottir (1999). The species was collected in the upper littoral conglomerate of the Bulandshofdi interglacial

sediments Snaefellsnes found at (W Iceland). It was in a

molluscan assemblage together with the bivalves Mytilus 4. events. Figure Chronology of main The ages ofthe lavas un- edulis Linne, 1758 and islandica (Linne, 1767), as derlying the Tjomes beds (N Iceland) are from Aronson & well several other as shallow-water species. The shell- Saemundsson (1975); that of the Serripes Zone of the

at Bulandshofdi rest on eroded Tjomes beds is from Einarsson et al. (1967) and Albertsson bearing deposits glacially Cainozoic lavas and overlain lava sheet that has (1978). are by a

been K/Ar-dated as 1.1±0.12 Ma (Albertsson, 1976). The

sediments held be from the Middle Reid (1996) identified the specimen mentioned by are to Pleistocene, older than the lava that Morch as L. squalida, on account of its typical rounded slightly cover, nevertheless is

swollen last to be from the The whorls, more whorl, more impressed sutures, thought same interglacial stage. species

and ribs of identification confirmed David G. more raised irregular size as compared to L. (Figure 1c, d) was by

littorea (Figure le, f). He also identified the specimens that Reid in the Spring of2000 (pers. comm.).

Gladenkov et al. (1980) recorded from the Mactra Zone as The conclusion seems to be that the only confirmed

L. squalida. Recently, specimens of L. squalida have also occurrence ofL. littorea in Iceland is that from the Middle

been collected in horizon 9 of the Mactra Zone. Then the Pleistocene deposits at Bulandshofdi(Figure 4). -9-

Evolution and eral new in migration species the N Greenland Kap Knbenhavn ma- rine fauna, dated at 2.45 Ma (Simonarson et al, 1998). Shell characteristics, several anatomical details, allozyme Thus, the first appearance of L. littorea in the Red Crag frequency and mitochondrial DNA all Formation is isolated sequences suggest no event, but linked to a cooling that Recent the closest relative of Littorina ofconsiderable among species event (glaciation) global impact on marine littorea is L. squalida, now restricted to the Pacific (Reid, molluscs. the fossil record is 1996). Although hardly sufficiently Littorina littorea probably spread from the North Sea

complete to provide certain details of the to the speciation proc- present area ofdistribution during the Early Pleisto- ess, it that L. from the Pacific to Several outside the appears squalida migrated cene. occurrences present area show the Atlantic the Arctic at the latest that the is through , during species a sensitive indicator of climatic change. of the Mactra Zone of the older it reached deposition Tjomes beds, Thus, Iceland during a rather mild Pleistocene than 3.5 Ma (Einarsson et al., 1967). Apparently, the interglacial et about spe- stage (Chen al, 1995), 1.1 Ma ago. cies did not reach the North Sea and its area Britain, as Then it disappeared from Iceland, probably during the

occurrence in the Red as well in other Crag Formation, as following glaciation, and we have no indication of its re- British or continental formations has not been European turn during youngerinterglacial stages or during the Holo-

confirmed (Reid, 1996). Distinct Pacific molluscs have cene. Drifting of planktonic larvae or rafting of adults on been found both in the Mactra Zone and in the underlying floating algae, driftwood, or other pieces of debris from the

Early Pliocene Zone ofthe beds & North Sea the British Isles Tapes Tjomes (Durham area, or continental Europe 1967; Backman, 1979; Slmonarson al, MacNeil, et 1998). might have taken place from time to time. However, it is Marincovich & Gladenkov Furthermore, (1999) and more likely that after the disappearance of shallow-water

Marincovich an of the (2000) suggested early opening areas on the Iceland-Faroe Ridge and the Wyville Thom- between and Bering Strait, 5.5 4.8 and based their son between 3.3 and 2.4 the Ma, Ridge, Ma, currents only oc- conclusion the on occurrence of molluscs of Atlantic- carried the casionally larvae, or rafting, floating or swim- Arctic origin found in southern Alaska with North Pacific adults ming to Iceland, but mainly in a northeasterly direc- diatoms. This conclusion contrasts with studies tion into the previous Norwegian Sea (Simonarson, 1981). Thus, (Einarsson et al., Durham & that 1967; MacNeil, 1967) stepping-stone migration of L. littorea via Iceland during

an of suggested 4.1-3.1 Ma for the initial opening of the Late Pleistocene or the age Holocene, e.g. to North Amer- the Bering Strait. The well-documentedinvasionof Pacific is earlier ica, not as probable as dispersal. Although the molluscs into the Arctic and North Atlantic & (Durham present current system in the North Atlantic seems to make the of MacNeil, 1967) during deposition the uppermost passive pelagic dispersal from east to west rather improb-

Serripes Zone of the Tjdmes beds, older than 2.6 Ma there indications that (Al- able, are during early stages of the bertsson, 1978), evidently resulted from a change to north- last conditions deglaciation were different and may at that erly flow the when the Central through Bering Strait, time have facilitated such dispersal (Kellogg, 1980; Buck-

American became closed at about 3.5 et Seaway Ma (Back- land al, 1986). This might also have been the case dur-

man, 1979). ing earlier Pleistocene deglaciation periods.

The oldest fossil occurrence of Littorina littorea in the There has been much debate as to whether L. littorea is of the Red Crag Formation in East be- native upper part Anglia, or introduced in North America. Surprisingly, the tween 2.55 and 2.4 that the differen- Ma, strongly suggests oldest fossil occurrence in eastern North America is from

tiation of the the of the two species postdates opening the middle part of the last glaciation in SW Nova Scotia Strait. This vicariant Bering might support a speciation and (Wagner, 1977). Also, two specimens have been recorded

transformation ofan Atlantic isolate of L. into L. from sediment squalida beneath the surface of a beach terrace in

littorea, during the latest phases of the trans-Arctic/North northern where Norse house Newfoundland, a was built,

Atlantic migration (Reid, as a result of and 1996), possibly presumably predates the settlement (Bird, 1968). Sev- at the onset of and cooling major widespread glaciation at eral shells have also been found in two Indian middens in about 2.5 Ma et al, Chen Nova and (Shackleton 1984; et al, 1995). Scotia, two more in New Brunswick, radiocar-

Since L. littorea has not been found in the Tjomes depos- bon-dated to between 1,000 and 1,500 BP (Clarke & Er- its, this transformation probably occurred after the tide of skine, 1961). These finds show that the local populations

the migration wave passed but to Iceland, apparently prior were established in northeastern America before European it reaching the North Sea and Britain. littorea Thus, L. settlement. Although L. littorea has not been found in possibly after 2.6 which indicates originated Ma, a some- North America in older deposits, migration earlier from what lower for the than cannot be age separation proposed by Europe excluded. On the other hand, it is not

Zaslavskaya et al. (1992), who placed the at that separation impossible repopulation from Europe might have oc- 3.45 Ma. The onset ofthe extensive about 2.5 curred glaciation at occasionally, also after the last glaciation Ma is also an important event the of affecting diversity (Ingblfsson, 1992). Spjeldnaes & Henningsmoen (1963)

Mediterranean molluscs of at the tropical affinity begin- even came to the conclusionthat L. littoreawas introduced ning of the (Monegatti & Raffi, This to North America it is 2001). gla- by man. However, more likely that ciation also remarkably affected the of the mol- diversity Vikings introduced some live specimens that genetically luscs in the north, resulting in the first of sev- affected and the appearance strengthened native population that rap- - 10-

its of distribution. lit- G.M. & A.J. idly increased area As a result, L. Buckland, P.C., Perry, D.W., Gislason, Dugmore,

intertidal herbivore 1986, The pre-Landnam fauna of Iceland: a palaeontological torea became the dominant on many contribution. Boreas 173-184. also 15, rocky shores in the region. European shipping may Carlton, J.T. 1969. Littorina littorea in California(San Francisco the Gulfof have helped a native race to disperse from St and Trinidad Bays). Veliger 11,283,284. Lawrence (Clarke & Erskine, 1961; Clarke, 1971). The Chen, J., Farrell, J.W., Murray, D.W. & Prell, W.L. 1995. Times- records from the west coast ofNorth America are taken to cale and palaeoceanographic implications of a 3.6 m.y. oxy- accidental introductions with the bivalves Cras- represent Indian gen isotope record from the north-east Ocean (Ocean Mercenaria from the Atlantic Coast sostrea or (Carlton, Drilling Program site 758). Paleoceanography 10, 21-47.

1969). Clarke, A.H., 1971. Littorina littorea , inative or introduced? The

Biologist 53, 160-162.

Clarke, A.H. & Erskine, J.S. 1961. Pre-Columbian Littorina

littorea inNova Scotia. Science 134, 393- 394. Acknowledgements Durham, J.W. & MacNeil, S.F. 1967. migrations of marine through the Bering Strait region. Ln: We are most indebted to Dr David G. Reid (NHM, Lon- Hopkins, D.M. (ed.). The Bering Land Bridge, 326-349. for valuable advice and confirmationofidentification don) Stanford (Stanford University Press). ofL. littorea from Bulandshofdi W (Snaefellsnes, Iceland). Einarsson, T., Hopkins, D.M. & Doell, R.R. 1967. The stratigra-

In addition, we wish to thank Godtfred Hopner Petersen phy ofTjomes, northern Iceland and the history ofthe Bering

(Zoological Museum, Copenhagen) and Svend Funder Land Bridge. In: Hopkins, D.M. (ed.). The Bering Land

312-325. Stanford benefitted Bridge, (Stanford University Press). (Geological Museum, Copenhagen), as we Evans, R.G. 1948. The lethal temperature of some common Brit- much from being able to use the large molluscan collec- ish littoral molluscs. JournalofAnimalEcology 17, 165-173. tions ofthe museums, not in the least of Icelandic material. O. Fauna 452 Fabricius, 1780. Groenlandica, pp. Lipsiae Our sincere thanks also to Aever Johannesson for photog- (Rothe). raphy, and to Dr C. Marques da Silva (Departamento de Ferussac, A.E. de 1822. Tableaux systematiques des animaux Universidade de and Dr K.S. Petersen Geologia, Lisboa) 111 Paris mollusques, pp. (Bertrand). for their earlier (GEUS, Copenhagen) comments on an Feyling-Hanssen, R.W. 1955. Stratigraphy of the marine Late-

typescript. Pleistocene of Billefjorden, Vestspitsbergen. Norsk Polarin-

stitutt Skrifter 107, 1-186.

Fretter, V. & Graham, A. 1962. British prosobranch molluscs,

London References 755 pp. (The Ray Society). Fretter, V. & Graham, A. 1980. The prosobranch molluscs of

Britain and Denmark, 5. Marine Littorinacea. Journal K.J. 1976. K/Ar of Albertsson, ages ofPliocene-Pleistoceneglacia- Molluscan Studies, Supplement 7, 243-284. tions in Iceland with special reference to the Tjdrnes se- Funnell, B.M. 1995. Global sea-level and the (pen-)insularity of 268 of quence, northernIceland, pp. Cambridge (University Late Cenzoic Britain, hr. Preece, R.C. (ed.). Island Britain: a Cambridge) (unpublished PhD thesis). Quaternary perspective. Geological Society of London, Spe- .„ Albertsson, K.J. 1978. Um aldur jardlaga a Tjdmesi. Ndtturu- , r r 0 cial Publication 96, 3-13. fraedingurinn 48, 1-8. Furmell, B.M. 1996. Plio-Pleistocene palaeogeography of the Arnold, D.C. 1972. Salinity tolerances of some common proso- southern North Sea Basin (3.75-0.60 Ma). Quaternary Sci- branchs. Journal ofthe Marine Biological Association of the enceReviews 15,391-405, UnitedKingdom 52, 475-486. Gendron, R.P. 1977. Habitat selection and migratory behaviour Aronson, J.L. & Saemundsson, K. 1975. Relatively old of the intertidal gastropod Littorina littorea (L.). Journal of from structurally high areas in central Iceland. Earth and AnimalEcology AS, 77-92. Planetary Science Letters 28, 83-97. Gibbard, P.L., West, R.G., Zagwijn, W.H., Balson, P.S., Burger, Backman, J. 1979. Pliocene of DSDP sites 111 A.W., Funnell, B.M., Jefery, D.H., de Jong, J., van Kolf- 116 and from the North and the age of the schoten, T., Lister, A.M., Meijer, T., Norton, P.E.P., Preece, Northern Hemisphere glaciation. Stockholm Contributions in R.C., Rose, J., Stuart, A.J., Whiteman, C.A. & Zalasiewicz, Geology 32,115-137. J.A. 1991. Early and early Middle Pleistocene correlations in G.G. 1925. A Bardarson, stratigraphical survey of the Pliocene the southern North Sea Basin. Quaternary Science Reviews deposits at Tjomes, in northern Iceland. Det Kongelige Dan- 10, 23-52. ske Videnskabernes Selskab, Biologiske Meddelelser (4)5, 1- Gibbard, P.L. & Zalasiewicz, J.A. 1988 (eds). Pliocene-Middle 118. 195 Pleistocene ofEast Anglia. Field guide, pp. Cambridge Barsotti, G. & Campani, E. 1982. II Promontorio di Castiglion- (Quaternary Research Association). cello (LI): III. Rivenimento di una popolazione di Littorina Gladenkov, Y.B., Norton, P. & Spaink, G. 1980. Verknyi Kaino- littorea (L.), Prosobranchia. Quaderni zoi Islandii. Trudy Geologicheskogo Instituta, Akademiya del Museo di Storia Naturale di Livorno 3, 65-71. NaukSSSR 345, 1-116, Bird, J.B. 1968. Littorina littorea: occurrence in northern New- Maimer, F.W. 1920-1925. The Pliocene mollusca of Great Brit- foundland beach terrace, predating Norse settlements. Sci- ain, being supplementary to S.V. Wood’s Monograph of the ence 159, 114. Crag Mollusca, 2. Monograph of the Palaeontographical Broderip, WJ. & Sowerby, G.B. 1829. Observations on new or Society, London, 485-652 (1920); 653-704 (1821); 705-856 interesting Mollusca contained, for the most part, in the mu- (1923); 857-900 (1925); pis 57-65 (1921). seum of the Royal Society. Zoological Journal. London 4, Ingolfsson, A. 1992. The origin of the rocky shore fauna of Ice- 359-375, pi. 9. - 11 -

land and the Canadian Maritimes. Journal ofBiogeography Olivi, G. 1792. Zoologica Adriatica ossia catalogo ragionato 19, 705-712. animali del delle degli Golfo e Lagune di Venezia; preceduto Johansen, A.C. 1901. On the variations observable in da dissertazione some una sulla storia fisica e naturale delGolfo: northern species ofLittorim. e Videnskabelige Meddelelserfra accompagnato da Memorie, ed osservazioni difisica storia Dansk naturhistorisk i 53, 295-307. naturale ed 334 Bassano. Forening Kjohenhavn economia, pp.

H.E. & I.E. 1995. Jonsdottir, Bjomsdottir, Setldg og saedy- Oskarsson, I. 1973. Nokkrar fagaetar skeldyrategundir vid Island.

nutima rafdnur fra sidjokultima og byrjun i Dalasyslu,.86 Ndtturufraedingurinn43, 154-161.

BSc pp. Reykjavik (University of Iceland) the- Reid, D.G. 1996. and evolution Littorina, 463 (unpublished Systematics of pp. sis). London (The Ray Society). T.B. 1980. and Kellogg, paleo-oceanography Rozycki, O. 1991. Mollusca. In: Klekowski, R.Z. & Weslawski, of the and Greenland Seas. Norwegian Glacial-interglacial J.M. (eds). Atlas of the marine fauna of southern Spitzber- contrasts. Boreas 9, 115-137. gen, 2, 358-541. Gdansk (Institute of Oceanology, Polish Knipowitsch, N. 1900. Liber die postpliocaenen Mollusken und Academy of Sciences).

Brachiopoden von Spitzbergen, Bulletin de I’Academic im- E.E. 1967. Sandison, Respiratory response to temperature and perial desSciences de St. Petersbourg 12,377-386. tolerance temperature of some intertidal gastropods. Journal Leifsdottir, O.E. 1999. nordanverdu Isaldarlbg a Snaefellsnesi. ofexperimental marine Biology andEcology 1,271-281. skeldyrafdnur, 101 of Setldg og pp. Reykjavik (University Shaddeton, N.J., Backman, J,, Zimmerman, H., Kent, D.V., Hall, Iceland) (unpublishedMSc thesis). M.A. Roberts, D.G., Schnitker, D., Baldauf, J.G., Desprai- Leifsdottir, 6.E. & L.A. 1999. Simonarson, Nakudungslog a ries, A., Homrighausen, R., Huddlestun, P., Keene, J.B., 68, 209- Stokkseyri og Eyrarbakka. Ndttiirufraedingurinn Kaltenback, A.J., Krumsick, K.A.O., Morton, A.C., Murray, 224. J.W. & Westberg-Smith, J. 1984. Oxygen isotope calibration

C. von 1758. naturae tria Linne, Systema per regna naturae, of the onset of ice-rafting and history of glaciation in the secundum classes, ordines, genera, species, cum characteri- North Atlantic region. Nature 307, 620-623. bus, locis. Editio differentiis, synonymis, decima reformata, Slmonarson, L.A. 1981. Cerastoderma edule (Linne, 1767) and 1(1-2), iii + 824 Holmiae pp. (Laurenti Salvii). its migration to Iceland. Arctic and Alpine Research 13, 105-

C. tria Linne, von 1767. Systema naturae per regna naturae, 112. secundum classes, ordines, genera, species, cum characteri- Slmonarson, L.A., Petersen, K.S. & Funder, S. 1998. Molluscan bus, differentiis, locis. Editio duodecima synonymis, refor- palaeontology of the Pliocene-Pleistocene Kap Kabenhavn

mata, 533-1068. Holmiae North 1(2), (Laurenti Salvii). Formation, Greenland. Meddelelser om Gronland,

Marincovich, L. Jr 2000. Central American paleogeography Geoscience 36,1-103. controlled Pliocene Arctic Ocean molluscan migrations. Ge- Sparck, R. & Thorson, G. 1933. Marine Gastropoda Proso- 28, 551-554, ology branchia. The Zoology ofthe Faroes 3, 1-45.

Marincovich, L. Jr & Y.A. 1999. Evidence for an G. Gladenkov, Spaink, 1975. Zonering van het mariene Onder-Pleistoceen op

openingof the Strait. Nature 397, 149-151. van In: early Bering grand mollusken-fauna’s. Zagwijn, W.H. & van Maton, W.G. 1797. Observations to the natural Staalduinen, relatively chiefly C.J. (eds). Toelichting bij geologische over-

western history, and the counties zichtskaarten van picturesque, antiquities of Nederland, 118-122. Haarlem (Rijks made in ofEngland, the years 1794 and 1796, 1, xi + 336 Geologische Dienst).

pp. Salisbury (Easton). Spjeldnaes, N. & Henningsmoen, K.E. 1963. Littorina littorea:

C.T. 1830. methodica molluscorum of Menke, Synopsis generum an indicator Norse settlement in North America? Science

omnium et in Museo ad- specierum earum, quae Menkeano 141,275-276.

servantor; cum synonymia critica et novarum specierum di- Thoroddsen, T. 1892. Postglaciale marine aflejringer, kystter-

agnosibus, Editio altera, xii + 91 pp. i Pyrmonti. rasser og strandlinier Island. Geografisk Tidsskrift 11,209- Merklin, R.L., Zarkhidze, V.S. & Ilina, L.B. 1979. Opredelitel 225. morskihk Pliosen-Pleistosenobykh mollyuskov severo- Thorson, G. 1941. Marine Gastropoda Prosobranchiata. The vostoka evropeiskoi chasti SSSR. Trudy Paleontolo- Zoology ofIceland 4(60), 1-150. gicheskogo Instituta, Nauk SSSR 1-96. Akademiya 173, Vermeij, G.J. 1982. Environmentalchanges and the evolutionary 1868. Videnska- fvtorch, O.A.L. Faunula molluscorumIslandiae. history of the periwinkle (Littorina littorea) in North Amer- belige Meddelelser fra den Naturhistoriske Forening i ica. Evolution 36, 561-580. Kjohenhavn 20, 185-227. Wagner, F.J.E. 1977. Recent mollusc distribution patterns and Morch, O.A.L. 1871. On the Mollusca of the Crag-Formation of palaeobathymetry, southeastern Beaufort Sea. Canadian Iceland. GeologicalMagazine (8)9, 391-400. Journalof Earth Sciences 14,2013-2028.

Mohr, N. 1786. Forsg til en Islandsk med adskil- Naturhistorie, West, R.G., Funnell, B.M. & Norton, P.E.P. 1980. An early oekonomiske lige samt andre Anmcerkninger, 413 pp. Pleistocene cold marine episode in the North Sea: pollen and Ki0benhavn(Holm). faunal assemblages at Covehithe, Suffolk, England. Boreas Monegatti, P. & Raffi, S. 2001. Taxonomic diversity and strati- 9, 1-10.

graphic distribution of Mediterranean Pliocene bivalves. Wood, S.V. 1848. A of the monograph Crag mollusca, or, de-

Palaeogeography, Palaeoclimatology, Palaeoecology 165, scription of shells from the Middle and Upper Tertiaries of 171-193. the east of England, 1. Univalves. Monograph of the Palae- Morrison, R. & G. 1998. The Pliocene-Pleistocene Kukla, (Terti- ontographical Society ofLondon, xn + 1-208, 21 pis. ary-Quaternary) boundary should be placed at about 2.6 Ma, B.B. 1913. The the Woodward, life of Mollusca, 158 pp. London not at 1.8 Ma! GSA Today 8, 9. (Methuen).

H. & Norddahl, Asbjdmsdottir, L. 1995, Isaldarlok 1 Zagwijn, W.H. 1992. The beginning of the in Europe Hvamms&di. In: D. & Hroarsson, B., Jonsson, Jonsson, S.S. and its major subdivisions. Quaternary Science Reviews 11,

(eds). Eyjar i eldhaft, 117-131. Reykjavik (Gott mal). 583-591. - 12-

Zaslavskaya, N.I., Sergievsky, S.O. & Tatarenkov, A.N. 1992.

Allozyme similarity of Atlantic and Pacific species of Litto-

rina (Gastropoda: ). Journal of Molluscan Stud-

ies 58, 377-384.